1. Field of Invention
The present invention relates to a safety control structure for heating wire and, more particularly, to a safety control structure which can interrupt the power and stop heating up in order to ensure safety when the heater wire produces exceptionally high temperature, and is suitable for use with heating devices such as electric blankets and hot packs.
2. Description Of The Prior Art
Heating devices such as hot packs are very popular in the market. The heating of a heater wire is interrupted automatically after it is heated up to a temperature preset by the user to ensure safety, so that the heating temperature of the heating device can be maintained within a preset range so that the heating device can be used as a hot compress and its safety can be ensured.
In order to control the temperature effectively, U.S. Pat. No. 5,861,610 employs a positive temperature coefficient (PTC) element as the sensing wire to sense the changes in temperature, and a heater wire for heating up and temperature control. These techniques have already been disclosed in U.S. Pat. Nos. 6,300,597, 6,310,322 and 6,768,086. While U.S. Pat. No. 7,180,037 employs a time difference determinator circuit to continuously measure the phase-shift time of zero cross signals, and a controller to operate continuously to output control signals to render the circuit connected or interrupted. As a result, both heating up and temperature control are achieved.
The above-mentioned circuit structures mainly employ sensors and controllers to control the temperature. Nevertheless, the circuits for temperature control are rather complicated. The heater wire will continue to heat up when the electrical elements such as sensors and controllers are broken, which is dangerous to users.
The present invention of a safety control structure for heater wire aims to overcome the above drawbacks and disadvantages by ensuring the safety when the heater wire produces exceptionally high temperature.